Low Pressure Thermochemical Treatment Machine

ABSTRACT

The invention concerns a treatment machine for low pressure carburizing of metal parts comprising at least one carburizing temperature-setting cell ( 2 ), one carbon-enriching cell ( 3 ) and one carbon-diffusing cell ( 4 ), arranged in succession one after the other. The cells ( 2, 3, 4 ) are of standard shape and of length (L 1 , L 2 , L 3 ) adaptable and proportional to the duration of the treatment performed in each cell. Each cell ( 2, 3, 4 ) comprises a treatment zone ( 14 ) located between an input module ( 10   a ) and an output module ( 10   b ), each constituting a cold zone, thermally insulated from the treatment zone ( 14 ) of the corresponding cell ( 2, 3, 4 ). The machine ( 1 ) comprises means for driving forward and transferring parts between the cells, located in the input ( 10   a ) and output ( 10   b ) modules of the cells ( 2, 3, 4 ).

BACKGROUND OF THE INVENTION

The invention relates to a machine for thermochemical treatment of metal parts comprising at least one heating cell, one carbon enriching cell for enriching the surfaces of the parts to be treated, one carbon diffusion cell diffusing from the surface to the core of the parts, and at least one hardening cell, arranged in succession one after the other and having a length adapted to the duration of the treatment performed in each cell, the machine also comprising mechanical means for transferring and moving the parts from one cell to the next and insulating means to insulate the cells from one another during the different successive treatment phases.

STATE OF THE ART

Numerous thermochemical treatment systems exist for carburizing and carbonitriding metal parts, in particular systems in the form of a case with a solid cement, systems in non-controlled atmosphere, systems in controlled atmosphere with a constant carbon potential, or low pressure systems with a pressure of about 5 mbar to 20 mbar, sometimes even up to 100 mbar.

Carburizing and carbonitriding generally require a partial pressure of the carburizing gas, formed by a hydrocarbon, for example methane (CH₄), acetylene (C₂H₂) or propane (C₃H₈), and possibly a nitriding gas, for example ammoniac (NH₃). The carburizing operations, i.e. carburizing temperature-setting treatment, surface enrichment treatment and carbon diffusion treatment, are preferably executed under partial nitrogen pressure. To prevent any oxidation during the carburizing treatment and during transport to the hardening cell, the parts are not exposed to air at any time.

The hardening operation, which follows the carburizing treatment, consists in cooling the parts rapidly. It is performed either in a bath of oils or molten salts or in a stirred gas at high pressure, such as nitrogen, helium or various mixtures of neutral gases such as carbon dioxide or hydrogen.

These different operations, i.e. the different phases of the carburizing treatment, are generally performed in the same enclosure, hardening being performed in a separate cell.

The Patent EP-A-0922778, in particular, describes a thermal treatment installation comprising a plurality of cells designed for thermal treatment of a set of metal parts. The cells are all connected to a central enclosure at the same pressure as the treatment cells. The parts are transferred from one cell to another by means of transport and handling rails. After carburizing in the corresponding cell, the carburized parts are transferred to the hardening cell passing via the central enclosure, meaning that there is no contact with the ambient air.

Other installations are made up of independent cells connected to one another by a mobile cell whose function is to perform either the loading and transfer to the hardening cell operations, or the loading and transfer operations and at the same time hardening under pressurized gas.

Other installations comprise a single partitioned cell of the “driven plate” type comprising an input chamber and a hardening under gas cell.

In all cases of low pressure carburizing from 5 to 20 mbar, the phases of the carburizing treatment, i.e. at least a carburizing temperature-setting phase, a carbon enrichment phase of the surface of the parts, and a diffusion phase of the carbon from the surface to the core of the parts, are successively performed in one and the same cell or in a single partitioned cell comprising mechanical means for advancing and transferring the parts. The mechanical means are then situated in a hot zone.

Another type of machine is described in U.S. Pat. No. 3,662,996. The machine is a conventional gas-carburizing machine at atmospheric pressure and comprises one cell for each phase of the carburizing treatment, i.e. a carburizing heating cell, a carbon enriching cell for enriching the surfaces of the parts to be treated and a carbon diffusion cell for diffusing the carbon from the surface to the core of the parts. The cells are arranged in succession one after the other and the parts are moved from one cell to another to receive the carburizing treatment, the length of a cell being previously defined according to the required treatment time in the cells.

However, even if each phase of the treatment is performed in different cells, this type of machine can only function under certain conditions, in particular under high pressures. Moreover, the mechanical means for advancing and transferring the parts are situated in a hot zone, where the corresponding treatment is performed, and are not thermally insulated. Furthermore, this type of machine is difficult to integrate in existing production lines and the length of each cell can not easily be modulated according to the duration of the required treatment.

OBJECT OF THE INVENTION

The object of the invention is to remedy the above-mentioned drawbacks and to design a low pressure thermochemical carburizing or carbonitriding, treatment machine that is efficient, flexible and able to be easily adapted and integrated into mass production lines of parts.

According to the invention, this object is achieved by the appended claims and, more particularly by the fact that the temperature-setting, carbon enrichment and carbon diffusion cells are of standard shape and each comprise a low pressure treatment zone situated between an input module and an output module, the input and output modules each forming a cold zone thermally insulated from the treatment zone of the corresponding cell, the mechanical means for transferring and moving being situated in the input and output modules of the cells and the output module of a cell being connected to the input module of the adjacent cell.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features will become more clearly apparent from the following description of particular embodiments of the invention given as non-restrictive examples only and represented in the accompanying drawings, in which:

FIG. 1 schematically represents a top view of a first embodiment of a thermochemical treatment machine according to the invention.

FIG. 2 schematically represents a top view of an alternative embodiment of a thermochemical treatment machine according to FIG. 1.

FIG. 3 represents a cell of the thermochemical treatment machine according to FIGS. 1 and 2.

FIGS. 4 to 6 schematically represent top views of alternative embodiments of a thermochemical treatment machine according to the invention.

DESCRIPTION OF PARTICULAR EMBODIMENTS

With reference to FIGS. 1 to 6, the thermochemical treatment machine is a machine 1 for low pressure carburizing treatment of metal parts under a vacuum. The machine 1 comprises a plurality of treatment cells 2 to 5 arranged in succession one after the other. Each cell corresponds to a particular phase of the low pressure carburizing treatment and presents a standard shape and a length L adaptable according to the duration of the treatment required in the cell. The manufacturing technique of the cells is that of cold-wall vacuum furnaces enabling an operating pressure comprised between 10⁻¹ mbar and 30 mbar.

The machine 1 also comprises means for moving and transferring the parts from one cell to the next and closing means designed to insulate one cell from the adjacent cells during the different phases of the carburizing treatment. Transfer of the parts between the cells is performed at a predetermined pressure, i.e. the carburizing pressure, of about 5 mbar to 20 mbar. Pumping systems keep the three cells at the same pressure, including during the transfer periods.

In FIG. 1, the machine 1 comprises in particular a carburizing heating cell 2. The object of the treatment performed in the cell 2 is to increase the temperature of the parts to the required carburizing temperature of about 880° C. to 1050° C. This phase is performed at the carburizing pressure of about 5 mbar to 20 mbar, preferably with nitrogen. In particular cases, the pressure can be increased up to 100 mbar.

Downline from the carburizing heating cell 2, the machine 1 comprises a carbon enriching cell 3. The treatment performed in the cell 3 consists in enriching the surface of the parts in carbon or in carbon and nitrogen to increase the hardness of the parts after hardening. This enriching phase is preferably performed by injection of nitrogen or any other neutral gas at a temperature of about 880° C. to 1050° C. completed at regular intervals by injection of a cementing gas. The pressure in the cell 3 is for example about 5 mbar to 20 mbar depending on the cementing gas used.

After the carbon enriching cell 3, the parts are transferred to a final carbon diffusion cell 4. The treatment performed in the cell 4 consists in diffusing the carbon into the thickness of the parts from the surface to the core of the parts, at the required depth of the cemented surface and the required percentage of carbon at the surface of the parts. This phase of the treatment is performed at the same pressure as that of the carburizing heating cell 2 and carbon enriching cell 3. The temperature is adjusted, preferably between 880° C. and 1050° C., to enable a good penetration rate of the carbon into the parts and to obtain the optimum temperature of the parts before the hardening operation is performed.

The required treatment temperature inside the carbon diffusion cell 4 is preferably different from the required treatment temperature inside the carburizing heating cell 2 and carbon enriching cell 3.

Downline from the cells 2 to 4, the machine 1 also comprises a hardening cell 5 equipped with pressure-tight doors. For example, the cell 5 is a hardening cell performing gas quenching, oil quenching, salt bath quenching or quenching in any other system enabling the parts to be cooled at the required speed to obtain the required hardness.

In an alternative embodiment, not represented, the machine 1 can comprise a tempering cell downline from the hardening cell 5. The tempering phase is performed at a temperature for example of about 200° C. to 300° C.

Upline from the carburizing heating cell 2, the machine 1 also comprises an input chamber 6 designed to store the parts waiting to enter the cell 2 (FIG. 1). In this case, care must be taken to perform vacuum purging in the input chamber 6 so that the pressure in the chamber 6 is the same as that in the carburizing heating cell 2, before the parts are input, and to ensure that the air is almost totally purged.

In the alternative embodiment represented in FIG. 2, the machine 1 comprises a gas pumping system 7 connected by suitable means to the carbon enriching cell 3 and designed to remove the gases present in the cells 2, 3 and 4. Only the carbon enriching cell 3 contains cementing gases liable to contaminate the cells 2 and 4. The pumping system 7 therefore advantageously generates a gas flow in the direction of the arrows F1, from the carburizing heating cell 2 and the carbon diffusion cell 4 to the carbon enriching cell 3, which may be contaminated.

The machine 1 can also comprise a first independent pumping system 8 of the input chamber 6 and a second independent pumping system 9 of the hardening cell 5.

In a general manner, the three cells 2, 3, 4, corresponding to the three indispensable phases of low pressure carburizing treatment, are cold-wall cells so as to be cold, non-polluting and not dangerous. The parts designed to be cemented have to pass successively, in order, via all the low pressure carburizing treatment cells 2, 3, 4 arranged one after the other.

According to the invention, the cells 2, 3, 4 of the machine 1 are all shaped according to the same general model, of standard shape, adapted to each function (heating, enrichment and diffusion), and their length L is able to be modulated, which enables the treatment time of each cell to be adjusted precisely for a given treatment rate. Changing the rate notably enables different carburizing depths to be achieved. The length L of a cell is therefore proportional to the duration of the treatment performed in this cell.

Moreover, the temperatures can be adapted to enable precise adjustment of the characteristics to be obtained on the parts to be treated.

In FIG. 3 illustrating only the carburizing heating cell 2 of the machine 1 of FIGS. 1 and 2, the cell 2 comprises an input module 10 a whereby the parts to be treated enter, and an output module 10 b whereby the parts exit after treatment. The input module 10 a and output module 10 b are of standard shape and can each contain a load 11 of metal parts.

The cell 2 presents a longitudinal axis 12 oriented from the input module 10 a to the output module 10 b. The longitudinal axis 12 corresponds to the direction in which the loads 11 move, in the direction of the arrows F2, inside the cell 2.

Between the input module 10 a and the output module 10 b, the cell 2 comprises two identical standard intermediate modules 13 of the same length. Fitting several intermediate modules 13 between the input module 10 a and the output module 10 b enables the length L1 of the cell 2 to be varied. For example, for the carbon diffusion cell 4, the larger the number of modules 13 the greater the carburizing depth, at the same running rate of the loads 11 in the cell 4.

The standard modules 13 of the cell 2 constitute a low pressure treatment zone 14 within which the treatment proper to the cell 2 is performed. The treatment zone 14, preferably formed by standard modules 13 with cold walls, is confined and insulated from the input module 10 a and output module 10 b, which then constitute cold zones of the cell 2. The cold zones are thermally insulated from the treatment zone 14 by means for example of thermally insulated cooled doors 15 arranged between the input module 10 a and output module 10 b and the confined treatment zone 14.

For example, cooling of a door 15 is performed by means of a heat exchanger generating water circulation at the level of the door 15.

In FIG. 3, the input module 10 a and output module 10 b are of standard shape having a substantially U-shaped cross-section, and each comprise an opening in connection with the adjacent module 13 and three walls closing the end of the cell 2. In the particular embodiment represented in FIG. 3, the input module 10 a comprises an input orifice 16 situated on a wall of the input module 10 a parallel to the longitudinal axis 12 of the cell 2, and the output module 10 b comprises an output orifice 17 situated on a wall of the output module 10 b parallel to the longitudinal axis 12 and situated on the same side of the cell 2 with respect to the longitudinal axis 12. The loads 11 of the parts enter and exit via the same side of the cell 2.

The input module 10 a and output module 10 b each comprise for example an ejection system 18 designed to push and remove the load 11 from the corresponding module 10 a, 10 b and a buffer stopping system 19 designed to wedge the load 11 before removal. The removal system 18 and the buffer stopping system 19 constitute mechanical means enabling the parts to be moved and transferred between the cells and are advantageously located in the cold zones of the cells 2, 3, 4.

The running movement of the loads 11 inside the cells is performed by the loads 11 themselves which push one another forwards when a new load 11 is input. The treatment zone 14 thus does not contain any mechanical means for transfer or forward movement which are arranged only in the cold zones constituted by the input module 10 a and output module 10 b of the cells.

Placing the transfer means in the input module 10 a and the output module 10 b, i.e. at the level of the cold zones of each cell, results in particular in a better efficiency of the carburizing treatment and a better conservation of the characteristics of the parts between the cells.

Moreover, the carbon enriching cell 3 comprises neutral gas injection phases alternating with cementing gas injection phases, transfer of the parts between the cells advantageously being performed at the same time as the neutral gas injection phases. It is therefore necessary to provide a sufficiently long neutral gas injection time slot and to actuate the different transfer and advancement means accordingly so as to be able to transfer all the loads 11 along the machine 1. The cementing gases are thus confined only in the carbon enriching cell 3 and are not liable to contaminate the other cells 2 and 4.

In the particular embodiment represented in FIGS. 1 and 2, the carburizing heating cell 2 comprises two standard modules 13, the input orifice 16 and output orifice 17 of the cell 2 are parallel and located on the same side of the cell 2 with respect to the longitudinal axis 12.

The next carbon enriching cell 3, which comprises a single standard module 13, is arranged in such a way that the longitudinal axis thereof 12 is parallel and oriented in the same direction as the longitudinal axis 12 of the previous cell. The input orifice 16 of the input module 10 a is therefore arranged facing the output orifice 17 of the output module 10 b of the previous cell 2 and the output orifice 17 of the output module 10 b of the cell 3 is arranged on the same side of the cell 3 as the input orifice 16 of the input module 10 a with respect to the longitudinal axis 12.

Thus, the carbon diffusion cell 4, which also comprises two standard modules 13, is arranged parallel to the other two cells with its longitudinal axis 12 oriented in the same direction and aligned with the carburizing heating cell 2. The input orifice 16 and output orifice 17, respectively of the input module 10 a and output module 10 b, are therefore arranged on the same side of the cell 4 with respect to the longitudinal axis 12. The hardening cell 5 is connected to the output orifice 17 of the cell 4 and the input chamber 6 is connected to the input orifice 16 of the cell 2.

The arrangement of the machine 1, according to FIGS. 1 and 2, is therefore substantially in the shape of two L's facing one another, the parts moving in the cells in the direction of the arrows F2 (FIG. 1).

Moreover, the input module 10 a and output module 10 b of the cells 2, 3, 4 are advantageously arranged in such a way that they form connecting compartments 20 between two adjacent cells. The compartments 20 of the machine 1 can then comprise gas and pressure insulation systems 21 from one cell to the other during the treatment phases. They can also comprise check valve systems to control the gas flow between cells.

For example, the machine 1 comprises a pressure-tight door 21 arranged between the input module 10 a of the carburizing heating cell 2 and the input chamber 6.

In the alternative embodiment represented in FIG. 4, the low pressure carburizing treatment machine 1 comprises the three cells 2, 3 and 4 arranged in parallel manner one next to the other. The longitudinal axis 12 of the cell 3 is parallel and oriented in opposition with respect to the longitudinal axis 12 of the cells 2 and 4. The input orifice 16 of the input module 10 a of the cell 3 is arranged facing the output module 10 b of the cell 2, whereas the output orifice 17 of the output module 10 b of the cell 3 is arranged on the other side of the cell 3 with respect to the longitudinal 12 axis, facing the input module 10 a of the cell 4. This particular orientation in opposition of the input orifice 16 and output orifice 17 of the modules 10 a and 10 b of the cell 3 in particular enables the machine 1 to be arranged with a general shape substantially in the form of an S, with the cells 2, 3, 4 facing one another. This results in a large space saving, the overall length of the machine being relatively small.

Furthermore, the machine 1 can comprise a storage area 22 of the loads 11 at the beginning of the treatment cycle, awaiting input to the input chamber 6, and a storage area 23 of the loads 11 at the end of the treatment cycle, downline from the hardening cell 5 and awaiting removal, for example to another site.

In the alternative embodiment of the machine 1 represented in FIG. 5, the longitudinal axes 12 of the cells 2 and 3 are oriented in the same direction and the longitudinal axis 12 of the cell 4 is oriented in opposition with respect to the other two. The cells 3 and 4 are then offset with respect to the cell 2. The machine 1 therefore presents a larger overall length. This particular arrangement, substantially in the shape of a U, in particular enables the pumping systems 7, 8 and 9 respectively associated with the cells 3, 6 and 5 to be integrated into the machine 1.

The machine 1 can further comprise supervision, checking and/or control systems 24 adjoining the cells to check and/or control correct running of the carburizing treatment cycle.

The alternative embodiment of the machine 1 represented in FIG. 6 differs from the alternative embodiment represented in FIG. 5 by the number of standard intermediate modules 13 of the cells 2, 3 and 4. The cells in fact respectively comprise three, two and three standard modules 13 arranged between the input module 10 a and output module 10 b. This results in an increase of the time spent by the parts in the corresponding cell.

Starting from the layout of the machine 1 according to FIG. 5, it suffices to disassemble the output module 10 b of the cell 2, to add the additional standard module 13 and to reposition the output module 10 b. Adding the additional standard modules, 13 is performed in the same way for the cells 3 and 4. This particular layout illustrates the great flexibility and the ease of modification of the machine 1 according to the applications and the required treatment time.

In a general manner, for one and the same low pressure carburizing machine 1, the lengths L1, L2 and L3 (FIG. 1) respectively of the cells 2, 3 and 4 can therefore be different depending on the number of standard modules 13 which they comprise. Such a machine 1 can adapt easily according to the place it is installed and can take a plurality of different configurations. The machine 1 therefore presents a completely reconfigurable architecture according to the applications, the size of the installation location, and the required treatment time, particularly due to the shape of the standard input module 10 a, output module 10 b and standard intermediate modules 13 of each cell 2, 3, 4 of the machine 1. This results in particular in savings in time and space and gains in productivity.

Moreover, the machines 1 represented in FIGS. 4, 5 and 6 in particular enable the storage areas 22 and 23 to be positioned close to one another. This results in simpler and faster handling of the loads 11.

In an alternative embodiment, not represented, the machine 1 can comprise two hardening cells, downline from the cell 4, for example an oil hardening cell and a gas hardening cell or two gas hardening cells. In this case, the output module 10 b of the carbon diffusion cell 4 is different from the output modules 10 b of the other cells and comprises two output orifices 17 arranged on each wall parallel to the corresponding longitudinal axis 12 of the cell 4. The two hardening cells are then connected to the same output module 10 b, the parts being input either to the first or to the second hardening cell, before being removed after treatment.

In another alternative embodiment that is not represented, the machine 1 can comprise a cleaning cell of the parts, between the input chamber 6 and the carburizing heating cell 2, to prepare the parts designed to be cemented. For example, the cleaning cell is a washing or degreasing machine working at atmospheric pressure or possibly in partial pressure in vapor phase.

In another alternative embodiment, not represented, the machine 1 can comprise a convective preheating cell of the parts, upline from the carburizing heating cell 2. For example, the preheating cell is a convective preheating furnace designed to heat the parts to a temperature for example of about 300° C. to 500° C., before the latter are input to the carburizing heating cell 2. Convective preheating makes the heating homogeneous and causes in particular oxidation of the parts and a good activation of the surfaces thereof. This phase is performed in air at atmospheric pressure, preferably with a little additional nitrogen. The preheating cell also results in time saving, as the parts are able to spend less time in the carburizing heating cell 2 after preheating thereof. Once the preheating phase has been completed, the preheating cell is vacuum purged before the parts are transferred to the inside of the next cell.

In the case of use of a convective preheating cell, a pressure-tight door 21 has to be provided between the input module 10 a of the carburizing heating cell 2 and the preheating cell.

Whatever the embodiment of the machine 1 described above, the treatment machine 1 therefore presents the following advantages. The machine 1 is cold on the outside and non-polluting, on account of the cold walls of the treatment zones 14 of the cells 2, 3, and 4. As the cells 2, 3, 4 are of standard shape and of adaptable length due to the intermediate modules 13 and to the standard input module 10 a and output module 10 b, they can be installed in any existing machining workshop and in any mass production parts manufacturing installation. Productivity is therefore greatly improved. The flexibility of the installation also enables optional cells, in particular cleaning, preheating and tempering cells, to be inserted or not according to the production orders or the thermal treatments to be performed.

Furthermore, the mechanical means for transferring and moving the parts between the cells are only located in the cold zones of the cells, in the input module 10 a and output module 10 b. This results in a better efficiency of the low pressure carburizing treatment.

The invention is not limited to the different embodiments described above. In particular, the parts to be treated can be formed by sets of parts arranged on a support. The cells can have any suitable shape. The transfer and closing means can be formed by any suitable means enabling tightness and predetermined pressure properties to be ensured between two adjacent cells. The cementing gas can be propane or any other hydrocarbon able to be associated with the temperatures of the carbon enriching cell 3 to treat the surface of the parts.

The transfer and moving means located in the cold zone of the cells can be formed by any other removal system and a totally different buffer stopping system. Transfer between two adjacent cells being performed at predetermined pressure, the machine 1 can comprise additional means (not represented) for adjusting and controlling the pressure inside the compartments 20 in the course of treatment, if necessary, during the transfer phases.

After the tempering cell if the latter is installed, the machine can comprise additional transfer means (not represented) designed to transfer the parts to another finishing treatment machine for example (shot peening, rectification).

The cells 2 to 4 can comprise heating equipment, a gas injection circuit and pumping connectors for vacuum pumps (not represented).

In another alternative embodiment, not represented, carbonitriding treatment may be applied in the cells 3 and 4. The thermochemical treatment machine 1 is then a vacuum carbonitriding treatment machine with a diffusion cell 4 into which a nitriding gas is injected. For example, nitrogen enrichment can then be performed by introducing a gas such as ammoniac (NH₃) into the surface enrichment cell 3 and diffusion cell 4 at a rate to be determined according to the required result.

Operation of the machine remains the same as before, with the parts to be treated passing successively in each treatment cell. The cells also have the same configuration, with an input module, an output module and standard intermediate modules arranged between the modules so as to form a fully reconfigurable machine, according to the workshop, the applications and the required treatment time in the cells. 

1-15. (canceled)
 16. Machine for thermochemical treatment of metal parts comprising at least one heating cell, one carbon enriching cell for enriching the surfaces of the parts to be treated, one carbon diffusion cell diffusing from the surface to the core of the parts, and at least one hardening cell, arranged in succession one after the other and having a length adapted to the duration of the treatment performed in each cell, the machine also comprising mechanical means for transferring and moving the parts from one cell to the next and insulating means to insulate the cells from one another during the different successive treatment phases, machine wherein the heating cell, the carbon enriching cell and the carbon diffusion cell are of standard shape and each successively comprise an input module, a low pressure treatment zone and an output module, along a longitudinal axis, the output module of a cell being connected to the input module of the adjacent cell and the input module and output module each forming a cold zone thermally insulated from the treatment zone of the corresponding cell, the mechanical means for transferring and moving being situated in the input module and output module of the cells.
 17. Machine according to claim 16, wherein at least the input and output module of the heating cell and of the carbon enriching cell and the input module of the carbon diffusion cell are of standard shape.
 18. Machine according to claim 16, wherein, a longitudinal axis of each cell being oriented from the input module to the corresponding output module, each input and output module comprises at least one orifice, respectively an input and output orifice, situated on a wall of said module parallel to said axis, and the means for transferring the parts from each output module to the corresponding input module act perpendicularly with respect to said longitudinal axis.
 19. Machine according to claim 18, wherein the longitudinal axes of at least two successive cells are parallel, in the same direction and/or in opposite directions.
 20. Machine according to claim 16, wherein the treatment zone of each cell is made up of a corresponding number of standard modules of the same length arranged in series, so that the length of the cell is adapted to the duration of the treatment cycle to be performed in said cell.
 21. Machine according to claim 16, comprising gas pumping means connected to the carbon enriching cell and organized such as to create a gas flow from the heating cell and the carbon diffusion cell to the carbon enriching cell.
 22. Machine according to claim 16, wherein, the carbon enriching cell comprising means for injecting cementing gases in alternation with neutral gases, said means for transferring and moving the parts are actuated to perform transfer of the parts during injection of neutral gases.
 23. Machine according to claim 16, wherein said insulating means of each treatment cell are arranged in a cold zone, in the corresponding input module and output module, and that they thermally insulate the treatment zone from said input and output module.
 24. Machine according to claim 23, wherein said insulating means are thermally insulated and cooled doors.
 25. Machine according to claim 16, wherein the treatment zone of the heating cell, of the carbon enriching cell and of the carbon diffusion cell is made up of standard modules with cold walls.
 26. Machine according to claim 16, wherein the temperature in the treatment zone of the carbon diffusion cell is different from the temperature in the treatment zone of the heating cell and of the carbon enriching cell.
 27. Machine according to claim 16, wherein, the input module of the heating cell being connected upline to an additional treatment cell, said input module comprises a pressure-tight door.
 28. Machine according to claim 27, wherein said additional treatment cell, arranged upline from the heating cell, is a convective preheating cell.
 29. Machine according to claim 16, comprising a tempering cell downline from the hardening cell.
 30. Machine according to claim 16, comprising means for cleaning the parts upline from the heating cell. 